Computer-archived data on 35 medicated and 87 unmedicated hyperkinetic boys and on 67 of their normal classmates will be used to test hypotheses concerning: 1) a Stepwise Model for the development of substance experience; 2) the role of childhood individual factors (age, diagnosis, aggression, IQ, amd self-esteem deficits) in substance use and its escalation; 3) the role of childhood environmental factors (stimulant drug treatment, parent characteristics, peer attitudes, social isolation, SES, and urban residence) in substance use and its escalation; and 4) the contemporary correlates of adolescent marihuana use; and to examine communalities within important identified subgroups (e.g., those who have resisted the opportunity to use substances).